1. Field of the Invention:
The present invention relates to a keying input apparatus, and more particularly to a keying input apparatus used in electronic equipment such as an electronic calculator.
2. Description of the Prior Art:
A key board having a plurality of key switches is used for electronic calculators. The conventional key board is constructed such that a given voltage is commonly applied to one end of each key switch and the other end of each key switch is connected to the circuit body having storage, calculation and control functions. Therefore, terminals or pins the number of which corresponds to the number of the key switches are required for the circuit body, and accordingly, individual wirings corresponding to. the number of key switches are also required. An integrated circuit is used in the circuit body of an ordinary electronic calculator. However, such an integrated circuit becomes exceedingly expensive, as the number of terminals or pins is increased. Accordingly, it is necessary to minimize the number of the terminals or pins in order to minimize the cost of the integrated circuit.
In order to solve such technical problem, the present applicant has proposed several keying input apparatuses. In a typical apparatus embodying the present invention, the digit timing signals of the display device are supplied individually to one side of the key switches, and the other side of each of the the key switches are connected commonly to an integrated circuit. A circuit for generating coded signals for identifying a depressed key generates a corresponding coded signal in response to the digital timing signal fed through the depressed key. According to such a keying input apparatus, means are required to generate the digit timing signal and the coded signal in synchronism with each other, resulting in complex circuit construction within the integrated circuit.
Therefore, it is an object of the present invention to reduce the number of the terminals and the wirings provided in the circuit body in keying input apparatus, thereby providing coded signals for identifying a depressed key with a simple construction of the apparatus.